Abstract
Paleontology Thousands of fossilized footprints left on a 180-m-long stretch of flood plain in Alaska's Denali National Park and Preserve offer news clues to the lives of hadrosaurs, commonly called duck-billed dinosaurs. The impressions, made between 69 million and 72 million years ago, cluster within four size ranges that represent specific age groups in a multigenerational herd, report Fiorillo et al. About 84% of the tracks were made by adult and near-adult hadrosaurs, 13% by young probably less than 1 year old, and only 3% by juveniles—a rarity that suggests the species experienced a rapid growth spurt. The presence of juveniles also hints that the creatures spent their lives in the Arctic; the young would not have been able to migrate to and from warmer climates during wintertime. Geology 10.1130/G35740.1 (2014).
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